Having Lisp all the way down (well, almost -- the GC-stuff is in C) is also very cool. I can keep pressing M-. M-. M-. and end up in the SBCL internals (Lisp code!) when I want to know what's going on.

Scott mentions on c.l.l. he's making a new release of FSet this weekend.

I admit, that CL has a lot of great stuff (CLOS/MOP is really excellent), and Lisp all the way down is nice too, but I am tired if fighting with different implementations, libraries that won't compile, and old/esoteric design.

Clojure is clean, functional, and has a large library set which "just works" - it is by far the most painless Lisp I've ever worked with, if you can get used to the purely functional data types (you can, just use them like lists) and live temporarily without tail recursion (you can recur, of course, and regular old recursion is fine, it just will explode at some point).